In surveying, in particular land surveying, it is an object to determine geometrical properties of one or more target points, like coordinates, distances, and orientations. In most instances those properties have to be determined with respect to a known reference system, which can e.g. be defined by one or more known reference points, e.g. embodied by known and/or defined reference marks in vicinity. In many geodetic measurements for example, the surveying instrument is installed above a surface reference mark at ground or above an otherwise embodied, fixed reference—commonly by using a tripod supporting the surveying instrument in a practical and in particular human operable height above ground.
The most common surveying instruments nowadays are so called total stations, which can be described as enhanced embodiments of tachymeters, providing a motorized movement of the aiming direction of an opto-electrical distance measurement, in angular coordinates commonly oriented (at least substantially) horizontal and vertical. Those devices can thereby provide many automated functions and can e.g. comprise features like automatic target recognition (ATR), an image- or video-camera, a sighting unit, a telescope, a GPS-unit, a compass, a wireless remote control, a leveling unit, a visible pilot beam, infrared light emission and detection, a human machine interface, etc. Examples can e.g. be found in US 2007/104353, US 2009/024342, US 2015/176991, EP 1 836 457 or others. Optionally, the present invention can also be applied to other cognate types of surveying instruments such as e.g. Laser-Scanners, Laser-Trackers, classic Tachymeters or Theodolits, etc.
EP 2 998 701 proposes a method for initially installing a surveying instrument on a reference point in order to reference a surveying instrument center to a thereby defined known coordinate system. This stationing includes an approximate installing of the instrument, followed by using a laser distance meter exactly directed in vertical direction of the surveying instruments inherent coordinate system. This laser distance meter has to be exactly targeted to the reference point by tilting the surveying instrument. By determining tilt value and a distance value at the time when the reference point is targeted, a referencing of the tilted surveying instrument center to the reference point is established. Finally, the surveying instrument is leveled by mechanically re-adjusting the tilt, whereupon stationing space coordinates of the exactly leveled surveying instrument center after leveling are concluded based on the mechanical tilt adjustment which was required.
Above described method is done once at time of stationing, in order to speed up the stationing procedure compared to prior art, where the instrument had to be installed exactly vertically over the reference point and manual measurements of instrument height had to be taken. Such was burdensome as in general multiple iterations of leveling, vertical shifting, height measurement and re-checking are involved. Once such a stationing is established (classically or as proposed in EP 2 998 701), all the subsequent target measurements of this instrument setup are then based on those fixed stationing space coordinates of the surveying instrument center point.
A technical problem which is not at all considered in above mentioned document is the fact that only in theory this one time stationing is fixed, but practically it can deviate during measurement. For example, in many practical cases the surveying instrument—or more precisely the legs of the tripod (or the like) on which it is stationed—tends to sink into ground or to move slightly due to other influences during measurement such as heat, wind, etc. Therefore, also the corrected surveying instrument center point from above is potential not valid throughout all of the measurements taken in this installation.
A re-verification of this corrected surveying instrument center point according to the proposed method during the measurement is not mentioned, as such would obviously be burdensome, since according to the method, the instrument has to be tilted again to point at the reference point to take measurements and then has to be re-leveled again. Such is burdensome, especially when the leveling is done manually, and it would also be error-prone.
Yet, an even bigger disadvantage of a re-consideration of the above described method would be the fact that such would result in a NEW instrument center point as basis for the following measurements, which differs from the previous instrument center point. In surveying, it is preferred and established practice that the surveying instrument center is considered as a fix anchor, which remains fix during all of the measurements taken from this installation. The method of EP 2 998 701 results in new surveying instrument center points each time—which is not desirable in a surveyor view.